Which treatment option is available for gastric cancers with a PD-L1 mutation?

• A. Atezolizumab
• B. Pembrolizumab
• C. Nivolumab
• D. Ipilimumab

Answer: (B)

The key idea is that gastric cancers showing PD-L1 expression can respond to therapies that block the PD-1/PD-L1 immune checkpoint, which releases the brake on T cells and allows them to attack the tumor. Pembrolizumab is a PD-1 inhibitor that directly interrupts the PD-1/PD-L1 interaction, reactivating T cells against cancer cells. In gastric cancer, pembrolizumab has established clinical evidence and approvals for tumors that are PD-L1 positive, particularly after prior therapy, making it the most supported option among the choices for this biomarker-driven setting. While other drugs in the list also target the same immune pathway or related targets, pembrolizumab has the strongest, most relevant approval and data for PD-L1–positive gastric cancer. Ipilimumab (a CTLA-4 inhibitor) and the other agents either lack the same level of evidence in this specific context or are not standard first-line choices for PD-L1–positive gastric cancer.